Subcutaneous adipose tissue thickness alters cooling time during cryotherapy

Objective: To determine if differing subcutaneous adipose thickness alters the treatment duration required to produce a standard cooling effect during cryotherapy. Design: A 4-group, between-groups comparison in which the independent variable was skinfold thickness (0-10mm, 11-20mm, 21-30mm, 31-40mm) and the dependent variable was cooling time, defined as the treatment duration required to decrease intramuscular (IM) temperature 7degreesC from baseline. Setting: A sports injury research laboratory. Participants: Forty-seven volunteers with anterior thigh skinfold measurement of less than 40mm. Intervention: Topical cryotherapy (750g crushed-ice bag) to the anterior thigh to produce a typical cooling effect, defined as IM temperature at 1cm subadipose declining by 7degreesC. Main Outcome Measure: Cryotherapy treatment duration required to produce a standardized cooling effect in subjects with differing subcutaneous adipose thickness. Results: Analysis of variance revealed that mean time to cool IM tissues by 7degreesC differed across all groups, with cooling time increasing as adipose thickness increased. The mean +/- standard deviation cooling times were as follows: 31-40mm (58.6+/-11.7min), 21-30mm (37.8+/-9.6min), 11-20mm\ (23.3+/-6.7min), and 0-10mm (8.0+/-3.4min). Conclusions: During cold application, there is a clinically important direct relationship between adipose thickness and required cooling time. This relationship necessitates dramatic adjustments to cryotherapy duration to produce similar IM temperature changes. A 25-minute treatment may be adequate for a patient with a skinfold of 20mm or less; however, a 40-minute application is required to produce similar results in a patients with skinfolds between 21 and 30mm, whereas a 60-minute application is required for patients with skinfolds of 30 to 40mm.